In a typical communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, with each service area or cell area being served by a radio network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a “NodeB” or “eNodeB” (eNB). A service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio network node.
A Universal Mobile Telecommunications System (UMTS) is a third generation (3G) telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs and BSCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface. EPS is the Evolved 3GPP Packet Switched Domain. FIG. 1 is an overview of the EPC architecture. This architecture is defined in 3GPP TS 23.401 v.13.4.0 wherein a definition of a Packet Data Network Gateway (P-GW), a Serving Gateway (S-GW), a Policy and Charging Rules Function (PCRF), a Mobility Management Entity (MME) and a wireless or mobile device (UE) is found. The LTE radio access, E-UTRAN, comprises one or more eNBs. FIG. 2 shows the overall E-UTRAN architecture and is further defined in for example 3GPP TS 36.300 v.13.1.0. The E-UTRAN comprises eNBs, providing a user plane comprising the protocol layers Packet Data Convergence Protocol (PDCP)/Radio Link Control (RLC)/Medium Access Control (MAC)/Physical layer (PHY), and a control plane comprising Radio Resource Control (RRC) protocol in addition to the user plane protocols towards the wireless device. The radio network nodes are interconnected with each other by means of the X2 interface. The radio network nodes are also connected by means of the S1 interface to the EPC, more specifically to core network nodes such as the MME by means of an S1-MME interface and to the S-GW by means of an S1-U interface.
The S1-MME interface is used for control plane between eNodeB/E-UTRAN and MME. The main protocols used in this interface are S1 Application Protocol (S1AP) and Stream Control Transmission Protocol (SCTP). S1AP is the application layer protocol between the radio network node and the MME and SCTP for example guarantees delivery of signaling messages between MME and the radio network node. The transport network layer is based on Internet Protocol (IP).
A subset of the S1 interface provided functions are:                S1-interface management functions such as S1 setup, error indication, reset and the radio network node and MME configuration update.        UE Context Management functionality such as Initial Context Setup Function and UE Context Modification Function.        E-UTRAN Radio Access Bearer (E-RAB) Service Management functions e.g. Setup, Modify, Release.        Mobility Functions for wireless devices in EPS Connection Management (ECM)-CONNECTED, e.g. Intra-LTE Handover and inter-3GPP-Radio Access Technology (RAT) Handover.        S1 Paging function.        Non Access Stratum (NAS) Signaling Transport function.        
Establishment of the S1-MME interface on S1AP protocol level is shown in FIG. 3 as the S1 setup procedure. The purpose of the S1 Setup procedure is to exchange application level data needed for the radio network node and the MME to correctly interoperate on the S1 interface. The radio network node may initiate the procedure by sending an S1 SETUP REQUEST message to the MME once it has gained IP connectivity and it has been configured with at least one Tracking Area Indicator (TAI). The TAI(s) are used by the radio network node to locate IP-addresses of the different MMEs, possibly in different MME pools. The radio network node includes its global radio network node identity and other information in the S1 SETUP REQUEST message. The MME responds with an S1 SETUP RESPONSE message. This S1 SETUP RESPONSE message includes for example the Globally Unique MME identifier(s) (GUMMEI) of the MME.
An Initial Context Setup process is shown in FIG. 4. An INITIAL CONTEXT SETUP REQUEST message is sent by the MME to request the setup of a UE context or context of a wireless device. This INITIAL CONTEXT SETUP REQUEST message comprises information related to both the UE context and different E-RABs to be established. For each E-RAB the MME includes E-RAB Quality of Service (QoS) parameters such as QoS Class Identifier (QCI) and Allocation and Retention Priority (ARP). The QCI is a scalar that is used as a reference to radio access node-specific parameters that control bearer level packet forwarding treatment, e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc., and that have been pre-configured by the operator owning the radio network node. An INITIAL CONTEXT SETUP RESPONSE message is sent by eNB to the MME confirming the setup. Current assumption is that the RAN-CN split is similar for 5G as for 4G, implying an (evolved) S1 interface.
Radio Resource Control (RRC) States
RRC, which is terminated in the radio network node on the network side from the wireless device, performs functions like:                Broadcast        Paging        RRC connection management        Resource Block (RB) control        Mobility functions        Wireless device measurement reporting and control        
The RRC states are:                RRC_IDLE        RRC_CONNECTED        
A wireless device is in the RRC_CONNECTED state when an RRC connection has been established between the wireless device and the radio network node. If this is not the case, i.e. no RRC connection is established, the wireless device is in the RRC_IDLE state.
EPS Mobility Management (EMM) and EPS Connection Management (ECM) States
The EPS Mobility Management (EMM) states describe the Mobility Management states that result from the mobility management procedures e.g. Attach and Tracking Area Update procedures.
Two major EMM states are:                EMM-DEREGISTERED        EMM-REGISTERED.The EPS Connection Management (ECM) states describe the signaling connectivity between the wireless device and the EPC, which includes both RRC connection between the wireless device and radio network node and S1 connection, i.e. S1AP association, between radio network node and MME.        
Two major ECM states are:                ECM-IDLE.        ECM-CONNECTED.        
In general, the ECM and EMM states are independent of each other. Transition from EMM-REGISTERED to EMM-DEREGISTERED can occur regardless of the ECM state, e.g. by explicit detach signaling in ECM-CONNECTED or by implicit detach locally in the MME during ECM-IDLE. However there are some relations, e.g. to transition from EMM-DEREGISTERED to EMM-REGISTERED the wireless device has to be in the ECM-CONNECTED state.
The wireless communication industry is at the verge of a unique business crossroads. The growing gap between capacity and demand is an urgent call for new approaches and alternative network technologies to enable mobile operators to achieve more with less. Today, mobile broadband data is growing at an annual rate of 40-50 percent per year in the U.S. and other regions globally. Mobile service providers address these rapidly expanding traffic volumes through deployment of additional network functions, which will be a significant capital expenditure (CAPEX) challenge. The nature of the mobile broadband data traffic is also evolving with new services including new video applications, connected cars and the Internet of Things (IoT). This rapid capacity growth and increasing traffic diversity in LTE networks stresses the assumptions of existing network architectures and operational paradigms.
Network Functions Virtualization (NFV) provides a new path that can increase the flexibility required by mobile service providers and network operators to adapt and accommodate this dynamic market environment. NFV is a new operational approach applying well-known virtualization technologies to create a physical Commercial Off-the-Shelf (COTS) distributed platform for the delivery of end-to-end services in the context of the demanding environment of telecom network infrastructure and applications.
Because EPC is critical to the realization and management of all LTE traffic, it is important to consider use cases related to virtualization of the EPC elements. Each individual EPC element also has specific considerations that determine whether to deploy with NFV. Virtualized EPC (vEPC) is a good example: Multiple virtualized network functions (VNF) can be deployed and managed on a Network Functions Virtualization Infrastructure (NFVI) but must cater to performance scalability in both signaling/control plane and user plane, each potentially demanding different levels of NFVI resources.
vEPC elements can benefit from more agile deployment and scalability. However, virtual resource monitoring and orchestration, along with service awareness, are essential for implementing elasticity effectively. Due to the nature of telecom networks, service Level Agreements (SLA) will be a key issue for a virtualized mobile core network. Because virtualization usually leads to a performance trade-off, equipment vendors must optimize data-plane processing to satisfy carrier-grade bandwidth and latency requirements and sufficient control-plane performance for SLAs needed to ensure availability of regulatory services, such as emergency calls.
VNF is a virtualized network function which serves as a VNF Software for providing virtual network capabilities. A VNF could be decomposed and instantiated in roles such as Virtualized MME (vMME), Virtualized PCRF (vPCRF), Virtualized SGW (vSGW) or Virtualized PDN-GW (vPDN-GW).
NFV is seen as an enabler for network slicing that is described herein.
When looking at the wide range of applications and use cases that are addressed with a 5G network, it is quite obvious these cannot effectively be addressed with a traditional approach of having a purpose built network for each application. This will lead to high cost for networks and devices as well as inefficient use of valuable frequency resources. An operator may have one physical network infrastructure and one pool of frequency bands, which may support many separate virtualized networks, also called network slices. Each network slice may have unique characteristics for meeting the specific requirements of the use case/s it serves.
A key function of 5G Core network is to allow for flexibility in network service creation, making use of different network functions suitable for the offered service in a specific network slice, e.g. Evolved Mobile Broadband (MBB), Massive Machine Type Communication (MTC), Critical MTC, Enterprise, etc.
In addition to Service optimized networks there are more drivers for Network slicing, such as;                Business expansion by low initial investment: Given the physical infrastructure it is much easier to instantiate another Packet Core instance for the business expansion than to set up a new parallel infrastructure or even integrated nodes        Low risk by no/limited impact on legacy: As the new instance is logically separated from the other network slices, the network slices can also provide resource isolation between each other. Thus introduction of a new isolated network slice will not impact the existing operator services and therefore only provide low risk        Short Time To Market (TTM): The operators are concerned about the time it takes to set up the network for a new service. Slicing of the network for different services/operator use cases provides a separation of concern that can result in a faster setup of a network slice for a certain service as it is separately managed and with limited impact on other network slices        Optimized use of resources: Today the network is supporting many different services but with new use cases and more diverging requirements there is a need for optimizing the network for the specific type use case. Network slicing allows to match services to optimized network instances, and it also allows for a more optimized use of those specific resources        Allows for individual network statistics: With service specific network slices and possibly even on the level of individual enterprises, there is a possibility of collecting network statistics specific for a limited and well defined group of users of the network slice. This is not the key driver for slicing but rather a benefit that may be a useful tool        
Slicing can also be used to isolate different services in an operator's network. Future networks are expected to support new use cases going beyond the basic support for voice services and mobile broadband currently supported by existing cellular network, e.g. 2G/3G/4G. Some example use cases include:                Evolution of MBB                    Evolved communication services            Cloud services            Extended mobility and coverage                        Mission critical Machine Type Communication                    Intelligent traffic systems            Smart grid            Industrial applications                        Massive Machine Type Communication                    Sensors/actuators            Capillary networks                        Media                    Efficient on-demand media delivery            Media awareness            Efficient support for broadcast services                        
These use cases are expected to have different performance requirements, e.g. bit-rates, latencies, as well as other network requirements, e.g. mobility, availability, security etc., affecting the network architecture and protocols.
Supporting these use cases could also mean that new players and business relations are needed compared to existing cellular networks. For instance it is expected that future networks should address the needs of                Enterprise services        Government services, e.g. national and/or public safety        Verticals industries, e.g. automation, transportation        Residential users        
These different users and services are also expected to put new requirements on the network. FIG. 5 shows an example of a network slicing for a case when there exists different network slices in the core network for MBB, Massive MTC and Critical MTC. In other words, the network slices may comprise separate core network instances supporting the different network slices.
Network slicing introduces the possibility that the network slices are used for different services and use cases and there is a need to enable usage of this mechanism for wireless devices using more than one network slice in the communication network to improve the performance of the communication network.